Electric speedometer



BEST AVAILABLE COF- H. M.NoRMAN ELECTRIC -S-IIEEDOMETEH Jan', 18,1944.

5 Sheets-Sheet l BEST lAWAMBLE COPS R. Nm A mm om N. .c. M m T H Ec .LvE ,4, 4 9 1 8, 1 ,fa .J

VFiled-Dea. 5, '1938 5 sheets-sheet 2 v BEST AvAxLABLE com H. M. NORMANELECTRIC SPEEDOMETER Jan, 18,1944.

' SSheets-Sheet 3 Filved Dec. 5,- 1938 B Kauai@ *MM a5 BEST'AVAILALECOPY Jan'. 18,1944. H, M', NORMAN 2,339,743

l Y l LEQTRIC SPEEDOMETER Filed Dec.l 5; 1938 s sheets-sheet 4BESWMLMCOP ELECTRIC SPEEDOMETER Jan. r18,'*1944- 2,339,743 f@ Fil-edDec. 5', 1938 5 Sheng-sheet 5 Patented 18, 1944 BEST AVAILABLE COPELECTRIC SPEEDOMETER Horace M. Norman, Niles Center, Ill., assigner toStewart-Warner Corporation, Chicago, 111., a corporation of VirginiaApplication December s, 193s, serial No. 243,977

27Claims.

The present invention relates to electric speedometers and isparticularly concerned with the provision of a new and improved electricspeedometer adapted to be installed as part of the standard factoryequipment of an automotive vehic e.

It has long been recognized thatelectric speedometers possess a numberoi advantages that Y the obtaining ot a quicker response as well asmoreaccurate readings. Another advantage of electric speedometers resides inthe fact that the mileage indicator or odometer may be located at adistance from the speedometer, thereby making it possible to provide amore advantageous distribution of the indicators upon 'the instrumentpanel.`

Despite the many advantages of electric speedl ometers, the latterhave-not been used extensively because of certain difiiculties. One ofthe more important of these is the undesirable effect upon the indicatorof variations in the potential of the battery from which thespeedometers are supplied with electrical energy and of temperaturevariations. l

One oi the primary objects of the present invention is to provide a newand improved electric speedometer requiring no external source ofenergy, such as a battery.

Another of the primary objects of the invention is to provide a new andimproved electric speedometer that is economical to manufacture. easy toinstall, easily calibrated to give accurate readings, and one that isnot likely to get out of calibration despite the usage to which it issubjected.

A further object of the invention is to provide an electric speedometerhaving improved means adapted to compensate for the eiTect of ambienttemperature variations and for the heating ei'- fect of the energizingcurrent upon the various circuit elements.

A further object of the invention is to provide an electric speedometerwith calibrating means whereby accurate readings may be obtainedirrespective of slight variations in electrical and magneticcharacteristics that may result in the course of manufacture of thespeedometer. The calibrating means of my invention contributesconsiderably to the decreased cost of manufacture as well as theimproved efciency of the speedometer.

A further object of my invention is to provide a new and improvedelectric speedometer or relatively small size whereby the cost ofmanufacture is substantially reduced.

A more speciilc object of the present inventio is to provide a new andimproved electric speedometer consisting of a sending unit, comprising aiixed armature winding and a rotatable permanent magnet, adapted togenerate a polyphase aliternating current and an indicator unit adaptedto be energized by the generated current comprising a fixed armaturewinding and an induction rotor rotatable thereby against a resilientrestraining member.

Another object of my invention is to provide an electric speedometerwith a. new and improved polyphase alternating current generator orsending unit, as it may be more aptly termed.

iAnother object of my invention is to provide an electric speedometerwith a new and improved electrically actuated indicator motor orindicator unit, as it may be more aptly termed.

Other objects and advantages of the present invention will becomeapparent from the ensuing description in the course of which referenceis had to the accompanying drawings in which:

Fig. 1 is a vertical axial cross sectional view through the polyphasealternating current sending unit;

Fig. 2 is a horizontal cross sectional view taken along the line 2-2 ofFig. 1 illustrating in detail the cam operated switch controlling theodometer;

Fig. 3 is a horizontal cross sectional view taken along the line 3-3 ofFig. 1;

Fig. 4 is a partial vertical cross sectional view taken along the line 44 of Fig. 2;

Fig. 5 is a view similar to Fig. 4 taken along the line 5-5 of Fig. 2;

Fig. 6 is a transverse cross sectional view taken along the line 6 6 ofFig. l;

Fig. 7 is a vertical axialcross sectional view through the 'indicatorunit;

Fig. 8 is a vertical transverse cross sectional view of the indicatorunit taken along the line 8--8 of Fig. '1;

Fig. 9 is a view similar to Fig. 8 taken along the line 9-9 of Fig. 7;

Fig. l is a view similar to the two preceding figures taken along theline iii-IU of Fig. '1;

Fig. 11 is a diagrammatic representation oi the electrical circuitsembodied in the present invention and showing, in particular, theelectrical connections between the sending unit, the indicator unit, andthe odometer. The rotors associated with the two units have been omittedfor purpose of simplicity since they are not conductively coupled to theillustrated electrical circuit;

Fig. 12 is a top elevation view of a modified form of rotor adapted tobe used with the sending unit to provide an improved alternating currentwave form; and

Fig. 13 is a plan view of a modified form of amature lamination adaptedto be used in the indicator unit. The amature windings have been showndiagrammatically.

Before proceeding with a detailed description of the sending andindicator units of the present invention, it is deemed advisable brieflyto describe the general nature of these units, the manner in-which theyare electrically connected to each other, and their location withrespect to the odometer and its associated circuit. Certain features ofthe sending unit and of an odometer are disclosed and claimed in adivisional application, Serial No. 484,589,'1ed April 26, 1943, andcertain features of the indicator unit are disclosed and claimed in adivisional application, Serial No. 484,590, also led April 26, 1943.

Referring, therefore, to Fig. 11, it may be noted the sending unit hasbeen indicated by reference character I0 and the indicator unit byreference character l2. These imita are connected to each other by threeinter-unit conductors I4, I6, and 20 of a length dependent upon therelative locations of the sending and indicator units. In rear-enginedvehicles the sending unit is located at the rear of the vehicle. and theindicator untis .located in the drivers compartment so that theindications may be readily observed by the operator. While the describedarrangement is particularly suited for rear-engined vehicles, its use isnot limited thereto, as it may be used just as well with a vehicledriven by an engine located at the forward end there- The sending `unitl0 is a polyphase, preferably a three-phase, alternating currentgenerator comprising the star-connected fixed armature winding 22, 24,and 26. These windings have associated therewith a salient polepermanent magnet rotor 30 (see Figs. 1 and 3) rotated by suitable meansat a speed bearing a constant relationship with the speed of the rearwheels of the vehicle, irrespective of whether the wheels are. driven bythe engine of the vehicle. 'I'he rotation of the rotor induces athreephase alternating current in the armature windings that is suppliedto the indicator unit through lse previously mentioned conductors I4, i6and The indicator unit also consists of three starconnected fixedamature windings 32, 3l, and 36, which, when supplied with alternatingcurrent, produce a revolving magnetic field, in a manner well known tothose skilled in the art. The revolving magnetic: field effects rotationof an induction rotor 40 (see Fig. '1). hereinafter termed a speed cup,the rotation of which is restrained by resilient means such as a spiralhair spring in a manner'to be described more definitely hereinafter. Thetorque exerted upon BEST AVAILABLE Coe` the speed cup is dependent uponthe magnitude and frequency of the alternating currents generated by thesending unit, and since both these characteristics are dependent uponthe speed of rotation of the permanent magnet rotor, it may be seen thatthe speed cup assumes a position dependent upon the speed of thevehicle.

The resistances of the armatures of both the sending and indicatorunits, as well as of the inter-unit conductors, are dependent upon theambient temperature and the value of the current flowing therethrough.In order to compensate for the effect of these temperature changes anumber of negative temperature coefficient series resistors areprovided, and these have associated therewith a shunt connected positivetemperature coeiicient resistor which, as will be explained hereinafter,performs another function, namely, that of adjusting the reaetance ofthe system. The negative temperature coelicient resistors are so locatedas to provide compensation even though the units may be located inregions where different 'temperatures obtain. For example, the sendingunit may be located, as in the usual installation, in a location whereit is subjected to outdoor temperatures which may range to aconsiderable value below zero degrees F. On the other hand, the sendingunit may be driven from the transmission of a rear-engined bus, wherethe temperature may rise to a value of approximately 200 degrees F. Theindicator unit, being located in proximity to the drivers compartment,is therefore in a region where the temperature remains in theneighborhood of '10 degrees F. The resistors are designed not only withphysical and electrical characteristics such that they providecompensation for changes in in the resistance of the windings but toovercompensate therefor, and thereby provide temperature compensationfor variations in the magnetism of the permanent magnet rotor of thesending unit and in the resistance of the induction type rotor of theindicator unit. Because of the nature of the negative temperaturecoefficient resistors which have a coe'iiicient that decreases in thehigher temperature ranges, it has been found desirable to utilizeadditional compensating means when the sending unit is located in a hightemperature region, as near the engine of a rear-engined bus. Theadditional compensation is provided by a stationary annular ringsurrounding the permanent magnet rotor of the sending unit made of metalhaving a characteristic such that its permeability is considerablygreater at low temperatures than at high temperatures. Either Simonds orMonel metal has been found satisfactory.

Referring again to Fig.11, it may be seen that the inter-unit conductorI4 is connected in series with a resistor 33 connected between winding25 and terminal 39 by conductors 42 and 43. Conductor I4 is connectedalso to terminal 44 of the indicator unit and the latter is connected towinding 36 by a, conductor 46.

Inter-unit conductor I6 is connected in series with resistor 48connected between winding 24 and terminal 50 by conductors 52 and 53.Conductor i6 is connected also winding 32 of the indicator unit througha terminal 54 and conductor 53.

Inter-.unit conductor 20 is connected in series with resistor 58.located in proximity to the indicator unit, as distinguished from thepreviously mentioned resistors 38 and 48 which are .located in proximityto the sending unit for reasons to be considered in detail hereinafter.Inter-unit conductor 20 is connected to the third winding 22 of thesending unit through terminal 60 and conductors 82 and 63. Interunitconductor 20 is connected to the third winding 34 o1' the indicator unitthrough terminal 64, conductor 65, the previously mentioned resistor 58.a zero temperature coeilicient calibrating resistor 88 and conductor 81.

Calibration of the indicator'unit is effected by the calibratingresistor 88 and an adjustable positive temperature coemcient calibratingresistor 68 connected directly across the interunit conductors I4 andI6, i. e., in lshunt to windings 32 and 36. The valve of the shuntresistance is controlled by an adjustable calibrating arm 10, one end ofwhich is in electrical contact with terminal 44. (See Fig. 8). Themanner in which calibration 'is effected by adjustment of the series andshunt resistors 86 and 88 to overcome slight variations in electricaland magnet characteristics resulting from manufacturing tolerances andvariations in material is described in greaterv detail hereinafter.

The number of inter-unit conductors is reduced by utilizing inter-unitconductor 20 to conduct battery currentutilized in actuation of theodometer 14, illustrated diagrammatically and comprising a solenoid 18..Since the odometer may be of the mual 'construction comprising a pawiand ratchet actuated counterv and an actuating solenoid. the odometerhas not been ldescribed or illustrated in detail. One terminal of-thesolenoid 18 is connected to inter-unit conductor` 20 by a conductor 18and ductor 20 through the previously mentioned conductor 82 and theother grounded' atr 92. Each. l time .the cam actuated contacts arebrought together, a complete energizing circuit vfor the solenoid 18 iscompleted through a circuit including, in part. thel ignition switch -84i in its closed position), the inter-unitconductor 20, and thecontacts.. Since'the battery supplies direct current, the batterycurrent is eifective only to operate the odometer because the sendingand indicator unitsare both insulated from ground. .It has'v been foundthat thebattery current has no appreciable eil'ect upon the reading oithe speedometer.

The physical construction of the sendingunit of my invention isillustrated in detail in Figs. 1 to 6. inclusive, to which reference is.had in the ensuing detailed description thereof. The sending unitcomprises. a metallic base detachably mounted upon an externallythreaded boss |02, preferably a part o f the transmission housing oi theautomotive vehicle, through which extends a shaft |04 rotating at aspeed directly proportional BEST AvAiLABLE coP.

the peening indicated by reference character |08. 'I'he housing issubstantially sealed against foreign particles and the like bydetachable rubber cover ||0 provided with a relatively long tubularopening H2' for a cable 4 enclosing the interunit conductors I4, i6 and20 which are connected, as previously described, to the terminal bolts38, 00 and 60 of the sending unit.

The space dened by the cup-like housing |06 is subdivided into agenerator compartment ||2 and a resistor and odometer cam and contactcompartment 4 by a relatively shallow metallic cup-like partition H6inserted directly into housing |08. The upper ends of the cup-likemembers terminate in concentric outwardly extendlng flanges ||8 and |20,whereby the two parts are readily held in fixed relationship withrespect to each other by an annular bezel |22. The latter.

'not only secures the two cup-like members together but also seals theupper end of the inner cup-like member I6 by a. combined terminal andresistor plate |24, preferably made of some material such as Bakelite. Aresilient sealing gasket |26 is interposed between the plate and theflange of the inner housing member.

The permanent magnet rotor 30 is fixedly secured to a verticallydisposed rotatable shaft |28 by a relatively short nonmagnetic bushing|30 attached to an enlarged portion |32 of the shaft, as by a press t.The rotor is held in place also by a shoulder |34 upon which it isseated and by the peened portion |36 of the bushing.

The rotor structure is illustrated best in Figs. 1

and 3', from which it may be seen to comprise an integral disc-like baseportion |38 and a plurality of substantially axially extendingspacedapart poles |40. The rotor consists of six poles, all magnetizeclsimultaneously to produce alt-er-- nate North and South poles, asindicated by the reference characters N and S in Fig. 3. The rotor ispreferably formed from a single flat piece' of magnetic steel bypunching and stamping operations and to insure proper positioningthereof with Arespect to the armature teeth, it is preferable that theinner axially facing surface thereof be ground and the bushing |30drilled with respect toit. In this connection it may be noted -it iseasier to drillthe bushingproperly than the hard metal of which themagnet is made.

Toprovide the additional Acompensation necessary to overcome thedecrease inthe magnetism of therotor Aai; high temperatures there isprovided a stationary annular ringv |4i surrounding the upper ends ofthe rotor poles where it is supported by a step in the housing |06. Itmay be secured in place by a suitable adhesive. The ring may be made ofSimonds or Monel metal or other metals the permeability of whichdecreases rapidly witli an increase in temperature. The ring, it may beobserved.' acts to shunt a portion of the flux produced bythe magnet.and the shunting effect is less at higher temperatures,

, whereby the*v additional compensation required to the speed oi thevehicle. The sending' unit` to supplement the resistors is obtained.

The` rotor shaft |28, which is provided with a pair of 'spacedfapartbearing surfaces |42 and |44, is journaled for rotation in a sleevebearing |46 provided with a radially extending and upwardly facingshoulder |48 at its lower end. The bearing |46 is mounted in a bearingbushing |50 xedly secured at its upper end to the bottom |52 of theinner cup-like member ||6 as by the peeping |50.v The bearing is of theoilless type, and is lubricated substantially for its life by means ofan annular oil-'saturated felt sleeve I 56 located BEST AVAILABLE COP"in a space between the bearing |46 and bushing |50. The felt sleeve isseatedupon the previously mentioned shoulder |48 and a centrally anddownwardly extending shoulder |58 formed at the upper end of the bearingbushing |50.

The rotor shaft |28 is held against substantial axial movementby thelower end of the bearing |46- and an externally'threaded bushing |60which are provided with bearing surfaces adapted to engage the oppositeends of the rotor bushing |30. 'I'he bushing |60 is adjustably mountedin the centrally threaded aperture |62 in the base member so that theend play of the shaft may readily be controlled. Bushing |60 is hollowedto receive the lower end of the shaft'|26.

A quickly detachable driving connection -between the magnet shaft andthe driving member |04 is provided by av square hollow |64at the lowerend of the magnet shaft and a complementary square driving portion |66at the upper end of the driving member |04.

'Ihe armature, which comprises the aforementioned windings 22, 24, and26, is ilxedly supported by the bearing sleeve |50 which is providedwith anoutwardly and downwardly facing shoulded |68 againstwhich thearmature laminations and end insulators |12 are held by a washer :|16over which'- portion -the lower end of the sleevevis peened, asindicated by reference character |18.

The armature laminations and likewise the insulating laminations |12comprise an apertured central hub portion V|80 and radially extendingsiibsiantially v'r-shaped teeth |82 around which are coiledthe'variouswindings 22, 24, and 26. The ilux densities in the armaturearerelatively low and the teeth may therefore .be made relav tivelynarrow, as illustrated. 'I'his results in a decrease in the amount ofwire required. From Fig. 3 where the lamination structurels best i1-lustrated, it may be seen that there are nine teeth and, therefore,since it is preferred that a three-phase winding be utilized. everythird coil is connected to form a phase winding. The end terminals ofallthree phases are connected together in a manner well known to thoseskilled in the art to form the neutral connection of a star-connectedarmature and the remaining terminals are brought out to the sending unitterminals, as described previously in connection with Fig. 11. Asubstantially sinusoidal wave form is provided by the illustratedconstruction of stator teeth and rotor illustrated and described above.

- Good results have been obtained by utilizing the speciednumber ofpermanent magnet poles and armature windings and by making the clearancebetween the magnet and amature teeth about .015 inch. l y v 'An improvedwave form is obtainable by slightly tapering the inner edges of thepermanent magnets |40, as illustrated in Fig. 12. In this figure the'rotor is indicated by the reference character 30'=and the permanentmagnet poles by the reference characters |4022. The inner edges |40A ofeach magnet |40' arevtapered slightly to-provide a more desirable fluxdistribution and thereby provide an improved wave form. It may be notedthat tapering the inner edges of the magnets affects the iluxdistribution the same as changes in the `form of the armature teeth.

' The odometer circuit controlling contacts are mounted inthe resistorand odometer cam and contact compartment I4 which is defined, it may beremembered, by the vinner cup-like housing.

'The contact structure comprises apair of resilient arms |86 and |88supported upon a raised platform |60 suitably stamped from the bottom|52 of the inner housing. The arms carry opposed tungsten contacts |82and |94 and the arms are so positioned with respect to each other thatthey normally are spaced apart to open the odometer actuating circuit,as indicated in Figs. 4 and 11. The lower arm |86 is made substantiallylonger than the upper arm in order that it may be moved upwardly intocircuit closing position by a cam |96 rotated at a speed proportional tothat of the magnet shaft and, therefore, proportional to that of thevehicle through gearing to be described shortly. The lower arm |86 ispositioned in electrical contact with the inner cas- Y ing ||6 and is,therefore, grounded through the latter. The two contact carrying armsare insulated from each other and from their securing screws |38 by apair of insulators 200 and 202 having bosses surrounding the screws. Theupper arm has its rear end bent at an angle upwardly, as indicated at204, to provide a terminal for the conductor 62.

The contact actuating cam |96, which is preferably made of some suitableinsulating material, is aiilxed to a cam shaft 286 journaled forrotation in a pair of upstanding apertured bracks ets 208 and 2I0. Thebracket 208 is formed by pressing up a portion of the bottom of theinner housing ||6 and the bracket 2I0 is preferablya right angledbracket, the horizontal portion 2l2 of which is mounted upon a raisedplatform 2|3 stamped lfrom the bottom |52 to which it is secured byscrew 2|4 in a position determined by a pair of dowels 2 l5.

The cam shaft 206 is rotated by a shaft 216 mounted above and at rightangles thereto in a bracket 2|8 formed integrally with the bracket2I0-2|2 and upon a punched-up bracket 220. Rotation of the magnet shaft|28 is transmitted to the cam shaft through (l) worm gearing 222 formedat the upper end of the magnet shaft, and helical gearing 224cooperatively associated therewith and formed intermediate the ends ofthe shaft 2|6; and (2) worm gearing 226 formed at the end of shaft 2|6,and helical gearing 228 formed` upon an enlarged portion of the c'amshaft 206.

The armature windings 26, 24, and 22 are conv nected by conductors 43,53. and 63 to, resistors 38, 48, and to conductor 62,'respectively.Conductors 43, 53, and 63 are brought out from the compartment ||2through the opening left by the punching of bracket ,220. and areinsulated from the metal of the inner housing ||6 by a rubber grommet230 (see'Fig. 2). Conductors 43, 53, and 62 are prevented from beingentangled with the gears in compartment H4 by a bracket 23| punched outfrom the side wall of housing H6 (see Figs.2and 4).

The combined terminal and resistor carrying insulator plate |24 supportsthe previously mentioned terminal bolts 39,- 50 and |50, which aresecured thereto by means of a plurality of lock washers and nuts 232.The yinter-unit conductors terminate in apertured terminals 234, whichare securely'fastened to the terminal bolts by nuts 235 and suitablelock Washers 236. The

secured to the insulating plate by rivets 242 (see Figs. l, 4 and 6).

The physical construction of the indicator unit is illustrated in detailin Figs. 7 to l0, inclusive. From Fig. 7 it may be seen that the unit isdivided into three compartments, namely, an indicator compartment 250,an amature and rotor compartment 252,-and a combined terminal andresistor compartment 254. Each of the compartments is formed of acentrally apertured cup-like housing suitably attached to the otherhousings, asbywelding. I

The combined terminal and resistor housing 254 comprises a cup-likemember 256 having fiattened sldes, the open' end of which is closed byan insulating plate 258 to which are secured the terminal bolts 44, 54,and 64. The plate, which has a shape corresponding to that of the member25B, is secured to the latter by bent-over fingers 260 and indentations262 adapted toengage opposite sides of the peripheral portion of theplate. The terminal bolts are secured to the plate by lock washers andnuts 264 andthe conductor terminals 265 are secured to the bolts by lockwashers and nuts 208.

'I'he negative temperature coemcient resistor 58 is supported upon apair of terminals 212 and 214. 'I'he former is secured inv position bythe terminal bolt 84 and the latter by a -rivet 218 extending throughthe insulating plate 208. The resistor is connectedv to these terminalsby suitable conductors in electrical conducting relationship with theresistor and the terminals.

The calibrating resistance 63 is preferably wound around a relativelywide strip 218 of insulating material spaced from the closure plate 258and secured in place by the terminal bolts 44 and 54. The ends of theresistor are connected to terminals 280 and 282, respectively, which arein electrical conducting relationship with the terminal bolts 44 and 54.'I'he calibrating arm10 is pivotally mounted for rotation upon the ter-I minal bolt 44 and is adapted, when rotated, to

vary the resistance in shunt across the terminals 44 and 54 withindesired limits, as necessitated by the electrical and magneticcharacteristics of the indicating and sending units. The' calibratingarm'is provided'with a silver contact 284 opposite the pivot end andwith an upwardly extending lug or projection 286 whereby it may bereadily rotated.

A length of resistance wire 08, having a substantially zero temperaturecoefiicient of resist ance,` is'attached at one end to the terminal 214and at the other to the conductor4 81 -which leads to winding 34 of thefixed armature.

The armature ,and rotor unit'252 consists of a casing 290,- thetransverse portion of which is spot welded to the transverse portion ofcasing 258. The bottoms are apertured centrally to receive a hollowbushing 292 provided with an outwardly facing shoulder 294 upon whichthe transverse portions -of ,the housings 256 and 290 rest and to whichthe latter are secured, as by the peening The armature, which comprisesthe fixed windings 32, 34, and 36. is mounted-upon an amature shaft 300made hollow for a reason appearing shortly, and provided with anintermediate enlarged portion 302 providing a shoulder abutting against'one end of the bushing 292. The armature shaft is detachably secured tothe bushing by a nut 304 threaded onto vthe left end thereof. The otherend ofthe enlarged portion 302 provides a shoulder upon which thearmature lami- BEST AVAILABLE COP.

nations 306 and a pair of end insulator laminations 300 are supported.An insulating bushing 3I0, one end of which rests against shoulder 294of the bushing, serves to insulate the armature windings from the shaft.The. right end of the armature shaft is provided with an enlarged hollowopening 3I2, the extreme end of which is peened over to secure thelamlnations in place.

The shape of the armature laminatlons is best illustrated in Fig. 9 fromwhich they may be seen to comprise a central hub portion 3i4 andradially extending generally T-shaped teeth 3I6 defining spaced-apartsubstantially elliptical slots 3l8.

'I'he armature windings 32, 34 and 36 are distributed in the slots,which are six in number, and each phase winding comprises a pair ofseries connected coils. The coils for one phase winding lie in slots l,3 and 4, 6, if it be assumed that the slots 3I8 are numberedconsecutively from 1 to 6 in a clockwise direction, as viewed in Fig. 9.The coils for the second phase winding lie in slots 2, 4 and 5.. I, andthe coils for the third phase winding lie in slots 3, 5 and 4. 2. Thewindings are so disposed that, when supplied with a threephasealternating current from the sending'unit, a two-pole revolving magneticfield is produced in a manner well known to those skilled in the art.

f This revolving field induces rotation of the previously mentionedspeed cup 40 provided with a relatively long portion 322 lying axiallyof the armature and spaced about .020 inch therefrom.

Laminations 324, concentrically arranged with respect to the armaturelaminations and surrounding a part of the axialy portion of the speedcup, provide a return path for the magnetic flux set up by the armaturewinding. The laminations are spaced about .020 inch from the speed cupand are held in fixed position by indented portions 326 of the housing290, which engage the opposite sides of the assembled laminations.

The speed cup is mounted upon a rotatable ndicator shaft 328 by aflanged bushing 330 securely aiiixed to the shaft and a bushing 332pressed upon the former. `Rotation of the speed cup may be limited by astop 336 mounted for rotation with the latter by the opposed flange 334and bushing 332, and co-operatively associated with a xed but slightlyresilient piano wire stop 338 secured to a relatively narrow indicatorshaft and dial support 340 attached to a peripheral radial ange 342formed integrally with the casing 290 by screws 34| in a positiondetermined by dowels 34 IA..

'I'he speed cup stops 336 and 330 may be eliminated, if desired.- byproper selection of hair spring. The spring could be strong enough toprevent rotation vof the speed cup more than a full rotation from itsnormal position. The elimination of the stop avoidsl certaininaccuracies at the lower speeds when the stops are moved out ofengagement with each other, when they have a tendency 'to sticktogether, and when moved, move with a sudden jerk.

The indicator shaft is journaled for rotation in spaced-apart combinedguide and thrust bearings 343 and 344 mounted in the armature shaft 300and in the support 340, respectively. The bearing 343 is mounted in'acup -346 tted into the enlarged opening 3I2 in the armature shaft sothat it may be easily removed therefrom by a suitable tool tting intothe smaller opening at the other end of the shaft. The bearing 344 ismounted in a bushing 350 threaded into the supa nut 352.

The rotation of the speed cup is restrained by a spiral hair spring 354,one end of which is attached to the indicator shalt and the other to anaxially extending projection 356 of an adinstable spring adjuster 358.The latter is mounted for rotation about the nut 352, and may be rotatedreadily by an axially extending proiection 360. The hair spring 354 iseffective to return the shaft to its normal position when the amature ofthe indicator unit is not supplied with an alternating current from thesending unit.

The front bearing and dial support 340 is made relatively rigid bybending portions 362 thereof rearwardly. The speed cup stop 338 isattached to the support by a pair of dowels 364 and a screw 365.

The indicator dial 30S-is attached to the opposite ends of support 340by a pair oi' screws 310. 'Ihe dial is apertured centrally so that theshaft may extend therethrough, and Lan indicator needle 312 is mountedupon the projecting end of the shaft. The dial is provided with suitableindicia, not shown, so that the needle indicates the speed of thevehicle as determined by the position of the speed cup.

The indicator compartment is formed by a cuplike housing 314 spot weldedto the ilange 342 of housing 290 and terminates in an outwardlyextending peripheral flange 318. An annular ring 318 having a flangesimilar to the flange 310 is held in fixed relationship with the flange'by a bezel 380, which acts also to hold in place the usual dial glass302. The glass 302 is resiliently heldin place between a relativelysolid annular gasket 384 and a hollow gasket 386.

The indicator unit as a whole may be mounted upon a suitable support,such as the instrument panel of arp-automobile (not shown) by a plu-;ality of extensior 390 welded to theihousing 'I'he armature windings ofthe above-described modification extend a substantial distance beyondthe ends oi the amature laminations. This difficulty can be avoided byutilizing the novel form of armature illustrated in Fig. 13. Referringnow to this figure, it may beseen that the windings are showndiagrammatioally upon an armature lamination 400. The important featuresof the illustrated construction are a decrease in the length oi wirerequired and in the distance the windings extend beyond the ends of thelaminations. These advantages are the result of locating the coilscomprising the various phase windings sov that no coil need be woundover another, as in the previously described construction. n y

The armature laminations comprise an apertured central hub portion 402and three identical radially extending portions 404 dividing into op'-.DOsed arcuate branches 406'. The branches 408 extend radially outward.as indicated by reference characters 408. and terminate in arcuateperipheral portions H facing each other. The described armaturelaminations .deiine two radially spaced apart groups of slots M2 and 4M.'I'he former are positioned adjacent the hub and the latter between theformer and the peripheral portion.

Each phase 'winding comprises a coil surrounding an inner radial portion40| of the amature laminations and one surrounding adjacent radialportions #08..the coils for one armature winding being indicated byreference characters M6 and M8, for a second by 420 and 422, and for theBEST AVAILABLE COP* third by 424 and 428. Like ends of the Windings arejoined together to form the neutral connection 428. The various coilsand phase windings are connected so as to produce a revolving magneticheld when they are supplied with threephase alternating current,substantially as indicated in Fig. 13.

Among the noteworthy advantages of my invention may be mentioned thesimplicity of manufacture of the various parts and the assembly thereofto form both the sending and indicator units. The various resistors andterminals are adapted to be mounted upon an insulating closure plateeasily attached to its associated unit. The armatures and armaturewindings are readily assembled as sub-units with their associated shaftsand these units are easily attachable to their respective housings. Therotors of the indicator and sending units are also easily assembled assub-units which may be readily positioned with respect to the othersub-units.

In operation the various windings and resistors of the indicator unit,the sending unit, and the odometer are connected electrically, asindicated in Fig. l1. When so connected and the permanent magnet rotorshaft 428 Vis connected to thel ductors i4, I6 and 20. The polyphasealternating currents flow through the fixed armature of the indicatorunit and produce a revolving ileld which induces rotation of the speedcup with a torque dependent upon the speed of the vehicle. Rotation ofthe speed cup is resisted by the spiral hair spring so that the speedcup assumes a position dependent upon the speed of the vehicle.

The described arrangement produces a deection of the indicator needlethat is not exactly a straight line relation to the speed of thevehicle, but the scale is so designed that a proper indication of thespeed is given at all times. The deflection of the indicator needle perunit change in speed decreases gradually at the higher and lower speeds.

The odometer 14 is actuated intermittently when the vehiclemoves andwhen the ignition v switch 04 is closed, as it ordinarily is when thevehicle is moving. Each time the cam (98 effects engagement of contacts|92 and |94. the solenoid is energized through a previously describedcircuit which includes the battery 82 and the interunit conductor 20.The direct current flowing through this circuit has no appreciableeffect upon the armature windings or upon the reading of thespeedometer.

The permanent magnet rotor of the sending unit is preferably rotated ata speed of 2,000 R. P. M.when the vehicle is traveling at a rate oi' 60M. P. H. This speed is, as known to those skilled in the art,approximately twice as fast as the speed of the permanent magnet rotorof a mechanical speedometer. Rotation of an integral permanent magnetrather than of a wound armature eliminates slip rings and brushes withtheir attendant wear, variable resistances and the like, and also thelikelihood of the windings being deleteriously aiected by long continuedr0- tation at high speeds.

BEST AVAILABLE COP*- assavis 7 While I have described an arrangementwherein the sending unit comprises a rotor having six poles and anarmature winding comprising nine teeth, each of which is encircled by100 turns of No. 26 dou-ble enamelled wire and adapted to be rotated atspeeds indicated above, these values may be modiiied. The indicator unitassociated with the sending unit comprises an armature, the phasewindings of which each consist of two series connected coils each having86 turns of No. 26 double enam'eiled wire. The phase windings of thesending unit armature have a resistance of about two ohms, measured fromterminal .to neutral and those of the receiving unit have substantiallythe same resistance.

The described construction and arrangement of the sending unit providesasubstantially sinusoidal wave form. However, slight variations from asine wave do not materially affect the operation of the speedometer as awhole, because the higher harmonics do not exert a substantial torquebecause oi' their high frequency. It is this factor, that is, theincrease in torque with increase in frequency (up to a certain value offreo uency and for further increases in frequency a decrease in torque),which 'governs the sending unit rotor speed. It is not desirable toincrease the fundamental frequency oi the generated current to high.

The negative temperature coefilcient resistors may all have identicalvalues, but since the manufacturing processes by which they are madeproduce slight variations the resistor 58 at the receivingunit is chosento have a resistance of approximately four ohms while the resistors atthe sending unit have values oi' about four and ve ohms. The zerotemperature coeillcient compensating resistor 66 has a value ofapproximately two ohms and the positive temperature coefncient resistorhas a. total value of about thirtytwo ohms and may be varied from thisvalue to about twenty-two ohms by the calibrating arm 10. The variousresistors may bemade from suitable materials presently available on themarket.

'Ihe negative temperature coecient resistors and the positivetemperature coeilicient shunt resistor function to` maintainsubstantially balanced the resistances of the armature windings,irrespective of variationsin their resistance because of changes inambient; temperature and of changes in temperature resulting fromvariations in current ow. The negative temperature coeicient resistorshave substantially the same physical proportions, and when located asdescribed, i. e., two at the sending unit and one at the indicator unit,then uniform results are obtainable when both units are located inregions where the temperatures are in the neighborhood of zero or 70degrees F., or when the sending unit is inaregion of zero degrees F. andthe indicator unit in a region of 70 degrees as in the usualautomobileinstallation. The locations could'be changed, and compensation providedby varying the values .,of the resistances, Ibut this would createunbalanced current conditions and these unbalanced conditions wouldresult in inaccuracies because the result of an unbalance may, ineffect, be divided into opposing torques on the induction rotorresulting in inaccurate readings. Small unbalances, it has been found.do not materially affect the readings.

Thenegative temperature coeflicient resistors at vthese'nding-unit' aredesigned to overcompensate for variations in resistance of the windingsbecause of temperature changes, i. e., they decrease the resistancesomewhat more than the resistance is increased by a rise in temperature,and vice versa. The effect of this overcompensation is to providecompensation for the effect of temperature changes upon the magnetism ofthe permanent magnet rotor, which decreases with an increase intemperature. A decrease in the strength of the magnetism upon anincrease in temperature results in a decrease in the magnitude of thecurrent but, since the resistance of the negative temperature coeiicientresistors decreases more than enough to compensate for the decrease inmagnitude resulting from an increase in the temperature of the windings,compensation is provided for the decrease in magnetism.

Negative temperature coefdcient resistors now available on the market(having a. resistance of 4 ohms plus or minus 10 per cent at 70 degreesF. and exhibiting a negative resistance change of .8 ohm plus or minus10 per cent for a. temperature change from 0 to 100 degrees F.) as wellas the usual negative temperature coeiiicient resistors made of carbonor carbon compounds exhibit a characteristic that varies with the rangein temperature. At lower temperatures the unit change in resistance perunit change in temperature is comparatively greater than at hightemperatures. It has been found that when the sending unit is placed ina region of 200 degrees F., the aforementioned resistors obtainable onthe market do not provide suiiicient compensation. An excellent way toprovide the additional compensation is by utilizing the annular xed ring14|, thevmagnetism of which decreases with increases in temperaturesuiliciently to provide the desired additional compensation. Since themagnetism is greater at lower temperatures than at higher, more of theflux available from the permanent magnet rotor is shunted from thearmature windings at lower than at higher temperatures. i. e., as thetemperature increases the decrease in the strength of the permanentmagnet is compensated for by decreasing the amount of flux shunted bythe ring.

It should be observed that the ring may be used. not only in conjunctionwith the negative temperature coeflicient resistors, but also in placethereof. By properly choosing a ring it may be made to overcompensate.that is, increase the effective magnet strength more than it isdecreased by a change in temperature, and vice versa, thereby tocompensate, at least in part, for changes in resistance of the armaturewinding.

The negative temperature coetdcient and positive temperaturecoefdcientresistors 58 and 65 at the indicator unit are also designedconjointly to effect similar overcompensation for resistance variationsand thereby compensate for variations in the resistance of the inductiontype rotor occasioned by temperature changes. The action of resistor 58is the same as that of the resistors heretofore described. The shuntresistor, even though it has a positive coeflicient, actually exhibitsthe characteristics of a. negative temperature coefcient resistorbecause of its location in the circuit. When the temperature increases,its resistance increases so that a lesser portion of the total currentflows through it, thereby to increase the portion of the current flowingthrough the armature winding.

The shape of the deflection-speed curve of the -indicator unit isgoverned by the ratio of the resistanceto the reactance in the circuitas a whole. This ratio can be adjusted by varying the values oi the.series resistance BB, the variation of which has no eiect upon thereactance, and o! the shunt resistance 88, the variation o! which isapparently the equivalent oi a change in resistance and reactance ot thecircuit. Consequently, it is possible readily and properly to calibratethe indicator for various types of hair springs as well as forvariations in the physical construction of units, which determine thereactance oi the system.

Ordinarily, calibrationmay be effected at three points, at a minimumpoint oi 10 M. P. H., where the indicator becomes effective,an-intermediate point of 30 M. P. H.. and at a high point of 60 M. P. H.The iirst calibration is governed by the hair spring and stop location.and the two others are obtained by selective variation of the tworesistors to make the deiiection-speed curve pass through the properpoints-i. e., to make the indicator read 30 and 60 M. P. H. when thevehicle is moving at these speeds. Y

While I have indicated my invention is applicable for indicating thespeeds o! automobiles, it

should be understood that this is its preferred use 'l and that Vtheindicator may be utilized to indicate the speeds of other movingobjects. However, there are particular advantages that make theinvention peculiarly adapted for use in vehicles.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. In` an indicator, the combination including, indicating means,electromagnetic means comprising an armature winding having a positivetemperature coefficient of resistance for operating said indicatingmeans, a source o! electrical energy including an armature windinghaving a positive temperature coeiiicient of resistance con.. nected incircuit with said first-mentioned armature winding for saidelectromagnetic means, and negative temperature coenlcient means incircuit with said armature windings adapted to compensate for variationsin resistance of the circuit occasioned by ambient temperature andcurrent variations. Y

2. In an indicator,the combination including, indicating means,electromagnetic means comprising a polyphase armature winding foroperating said indicating means, a source of electrical energy includinga polyphase armature winding connected in circuit with saidilrst-mentioned armature'winding 'for said electromagnetic means, saidwindings having positive temperature coemcients of resistance andbalanced impedances, and negative temperature coefficient resistancemeans in series with each of the interconnected phase windings adaptedto compensate for variations in resistance of the circuit occasioned byambient temperature and current variations i'or maintaining balancedcurrent conditions in the system.

v3. In a speed indicator for automotive vehicles, the combinationincluding, indicating means located in proximity to the driverscompartment, electromagnetic means comprising a three-phase armaturewinding for operating said indicating means, said electromagnetic meansbeing located in proximity to said compartment, a source of electrical.energy including a three-phase arma ture winding connected in circuitwith said irstymentioned armature winding for said electromagneticmeans, said last-mentioned armature winding being located at a distancefrom said other winding and in proximity to the vehicle er1- BESTAVAILABLE coP- gine, and negative temperature coeilicient resistancemeans in circuit with said windings adapted to compensate for variationsin the resistance thereof, certain of said resistance means beinglocated in proximity to certain ones of said armature windings.

4. In a speed indicator for automotive vehicles, the combinationincluding, indicating means located in proximity to the driver'scompartment, electromagnetic means comprising a three-phase armaturewinding for operating said indicating means, said electromagnetic meansbeing located in proximity to said compartment, a source of electricalenergy including a three-phase armature winding connected in circuitwith said firstmentioned armature winding for said electromagneticmeans, said last-mentioned armature winding being located at a distancefrom said other winding and in proximity to the vehicle engine, and anegative temperature coeilicient resistor in series with each of theinterconnected phase windings adapted to compensate for variations inresistance of the windings, one of said resistors being located inproximity to the rstmentioned armature winding and the other two inproximity to the second-mentioned armature winding. i

5. In an indicator, the combination including, indicating means,operating means therefor comprising a polyphase armature winding, meansincluding a second polyphase armature winding connected to saidilrst-mentioned winding for supplying the latter with energizingcurrent, and

resistance means electrically connected in shunt circuit relation withsaid windings for adjusting the reactance of the system.

6. In an indicator, the combination including, indicating means,operating means therefor comprising a polyphase armature winding, meansincluding a second polyphase armature winding connected to saidfirst-mentioned winding for supplying the latter with energizingcurrent, and adJustable resistance means in shunt and series circuitrelation with said windings for varying the effective resistance andreactance of the system.

7. In an indicator, the combination including, indicating means,operating means therefor comprising a star-connected three-phasearmature winding, means including a second star-connected three-phasearmature winding connected to said rst-mentioned winding for supplyingthe latter with energizing current, and means electrically connected incircuit with said windings for adjusting the eiective resistance andreactance of the system, said means including a reslstor connected inseries with one phase winding' of each armature and another connectedacross the two remaining phase windings of the armatures.

8. In an indicator, the combination including, indicating means,operating means therefor comprising a star-connected three-phasearmature winding, -means including a second star-connected three-phasearmature winding connected to said mst-mentioned winding for supplyingthe latter with energizing current, and means electrically connected incircuit with said windings for adjusting the effective resistance andreactance of the system, said means including a fixed resistor connectedin series with one phase winding of each armature and an adjustableresistor connected in shunt across the remaining phase windings ot thearmatures.

9. In apparatus of the type described, the combination including, anindicator unit comprising BEST AVAILABLE COF a star-connectedthree-phase armature winding,

.- aoource o! alternating current therefor comprising asimilar windingconnected thereto, and means including a aero temperature coeiilcientresistor in series with only one phase connection i'or controlling theresistance of the circuit.

10. In apparatus of the type described, the combination including, anindicator unit comprising-a star-connected three phase armature winding,a source oi alternating current therefor comprising a similar windingconnected thereto, and'means including' a resistor connected in shuntrelation across two phase windings or the armatures tor-controlling thereactance of the circuit.

ll. In apparatus of the type described, the combination including, anindicator unit comprising a fixed star-connected three-phasearmaturewinding, an annular induction type rotor adapted to be actuatedthereby and an annular field surrounding the latter, a source o1alternating current for energizing said armature winding to eieetrotation ofthe rotor including a similar armature winding connected tothe ilrstmentioned winding and a-permanent magnet rotor rotatablethereabout at a speed proportional toa characteristic to be indicated,and means for varying the proportion o! resistance to reactance in thecircuit, said last-mentioned means including a resistor connected inseries with one set of interconnected phase windings, and an adjustableresistor connected across the remaining sets of intercononected phasewindings.

12. In an indicator, the combination lincluding, indicating means,electromagnetic means comprising an amature winding for voperating saidindicating means, a source ot electrical energy for said'Yelectromagnetic means, said source including an' armature winding and acooperating magnetlc ilux producing rotor, said windings having positivetemperature coeiilcients of resistance, and negative temperaturecoeiiicient resistance means located in proximity to thesecond-mentioned armature winding so constructed and arranged as toovercompensate for the eilect of temperature changes upon theresistancev of the system, whereby said resistance means are eiective tocompensate lor, the effect ci temperature'changes upon said rotor.

13. In an indicator, the combination including, indicating means,electromagnetic means comprising an armature winding and an inductiontype rotor adapted to be rotated thereby for operating said indicatingmeans, a source of electrical energy for said electromagnetic meansincluding an armature winding connected in circuit with'saidfirst-mentioned armature4 winding, said windings having positivetemperature coeiilcients ci resistance. and negative and positivetemperature coeillcient resistance means located in* proximity to saidelectromagnetic operating means for compensating for variations in theresistance oi' the circuit occasioned by ambient temperature and currentvariations, said resistance means being so constructed and arranged asto overcompensate for the eii'ect of temperamre variations upon theresistance o! said system. whereby said resistors are etective tocompensate for the eect of temperature changes upon said induction typerotor.

14. In an indicator, the combination including, indicating means,electromagnetic means compxising al star-connectedthree-phase armaturewinding' and a rotatable induction type rotor for operating saidindicating means, a source of electrical energy for said armaturewinding including a star-connected three-phase armature windingconnected in circuit with the first-mentioned armature winding and apermanent magnet rotor adapted to be rotated at a speed proportional toa characteristic to be indicated, said windings having positivetemperature coeiiicients oi resistance, and negative temperaturecoefficient resistance means 1n series with each of the interconnectedphase windings adapted to compensate for variations in the resistance ofthe circuit occasioned by ambient temperature and current variations,two of said resistance means being located in proximity to thesecond-mentioned armature winding and the third in proximity to thedist-mentioned armature winding, said two resistance means being soconstructed and arranged as to overcompensate and said one as toundercompensate for variations in resistance resulting from temperaturechanges.

l5. In an indicator, the combination including, indicating means,electromagnetic means comprising a star-connected three-phase armaturewinding and a rotatable induction type rotor for operating saidindicating means, a source of electrical energy for said armaturewinding including a star-connected three-phase armature windingconnected in circuit with the first-mentioned armature winding and apermanent magnet rotor adapted to be rotated at a speed proportional toa characteristic to be indicated, said windings having positivetemperature coefllcients of resistance, negative temperature coefficientresistance means in series with each of the interconnected phasewindings adapted to compensate for variations in the resistance of thecircuit occasioned by ambient temperature and current variations, two ofsaid resistance means being located in proximity to the second-mentionedarmature Winding and the third in proximity to the mst-mentionedarmature winding. said two resistance means being so constructed andarranged as to overcompensate and said one as to undercompensate forvariations in resistance resulting from temperature changes, andpositive temperature coeiilcient resistance means connected across thetwo remaining phase windings of said mst-mentioned armature Winding,whereby the combined effect of said one negative temperature coeilicientresistance means and said positive temperature coeillclent resistancemeans overcompensates for variations in resistance resulting fromtemperature changes, said ,overcompensation being effective tocompensate for the eiiect of temperature changes upon said rotors.

16. In an indicator, the combination including, indicating means,electromagnetic means including an induction type rotor and a polyphasearmature windng for operating said indicating means, and a polyphasecurrent generator for supplying said electromagnetic means with currenthaving substantially a pure sine wave form, said generator including afixed polyphase starconnect'ed armature winding comprising spaced apartsubstantially T-shaped tooth deiining laminations, and a permanentmagnet rotor having spaced apart generally rectangular poles extendingaxially of the rotor shaft and in the direction of the teeth, thearmature facing surface of the rotor being substantially cylindrical,and the peripheral portions of the tooth deining laminations beingcurved toA a radius of curvature less than the radius of curvatLu-eofthe inner surface oi' the rotor.

17. In apparatus o! the type described, the combination including, analternating current generator including an amature winding and acooperating magnetic ux producing rotor, said winding having a positivetemperature coelcient of resistance, and negative temperature scemcientresistors located in proximity to said winding so constructed andarranged as to overcompensate for the etiect of temperature changes uponthe resistance of the winding, whereby said resistors are eilective tocompensate for the eilect of temperature changes upon said rotor.

18. In an indicator, the combinaiton including, an alternating currentgenerator including in combination an amature winding and a cooperatingmagnetic iiux producing rotor, said winding having a positivetemperaturecoeiilcient oi resistance, and a substantially ilxed annularring made of metal having a characteristic such that its magnetismdecreases substantially upon increases'in temperature, and vicev versa,in proximity to said ilux producing rotor to compensate for the eiect cttemperature changes upon the magnetism oi' said rotor.

19. In an indicator, the combination including, an alternating currentgenerator comprising an armature winding and a cooperating magnetic iluxproducing rotor, said winding having a posiJ tive temperature coemcientoi resistance..and a substantially iixed annular ring made ot metalhaving a characteristic such that its magnetisml decreases substantiallyupon increases in temperature, and vice versa, in proximity to said ilusproducing rotor'to compensate for thejei'iect of temperature changesupon the magnetism oi said rotor, said ring being so constructed that itovercompensates for the changes in magnetism of said permanent magnetrotor whereby it compensates, at least in part, for variations in .theresistance of said winding resulting from c in the temperature thereoi'.

20. In an indicator, the combination including. an alternating currentgenerator including in combination an amature winding and a cooperatingmagnetic iiux producing rotor, said wind ing having a positive'temperature coeiilcient of resistance, negative temperature coemcientresistors located in proximity to said 'armature winding so constructedand arranged asto compensate for the eiect' of temperature changes uponthe system, and a substantiallyiixed annular ring surrounding a portionci the permanent magnet rotor and having a characteristic such that itsmagnetism decreases substantially upon increases in temperature, andvice versa, whereby said resistors and ring -are effective tovcompensate for the effect of temperature changes upon the magnetism ofsaid rotor and the resistance of said winding.

21. In apparatus 'of the type described, vthe combination including, analternating current generator including in combination an armaturewinding and a cooperating magnetic nux producing rotor, said windinghaving a positive temperature coefiicient of resistance, and negativetemperature coefficient resistance means located in proximity tcsaidarmature winding. said resistance means having a characteristic suchthat the coeiilcient oi' resistance is greater in magnitude in a lowerthan a higher temperature'range,

and magnetic means located in proximity to said rotor constructed ofmetal, the permeability oi which decreases substantially for unitvariations in temperature in a high temperature range, whereby theresistance means and magnetic BEST AVAILABLE COP means are eilective tocompensatefor the effect oi temperature changes upon said rotor whensaid energy source is placed in a higher temperature region.

22. In an indicator, the combination including, indicating means',electromagnetic means comprising an armature winding for said indicatingmeans, a source of electrical energy for said electromagnetic means,said source including an amature winding and a cooperating magnetic uxproducing rotor, said windings having positive temperature coefllcientsoi resistance, and a substantially iixed annular ring made oi metalhaving a characteristic such that its magnetism decreases substantiallyupon increases in temperature, and vice versa, in proximity to said uxproducing rotor to compensate for the eiect of temperature changes uponthe magnetism or said rotor.

23. In an indicator, the combination including, indicating means,electromagnetic means comprising an armature winding for operating saidindicating means, a source of electrical energy for said electromagneticmeans, said source including an armature winding and a cooperatingmagnetic flux producing rotor, said windings hav` ing positivetemperature coefficients of resistance, and a substantially fixedannular ring made oi metal having a characteristic such that itsmagnetism decreases substantially upon increases in temperature, andvice versa, located in proximity to saidiiux producing rotor tocompensate i'or the eiiect o! temperature changes upon the magnetism otsaid rotor, said ring being so constructed that it overcompensates forthe changes in magnetism of said permanent magnet rotor, whereby itcompensates, at least in part, for variations in the resistance of saidwinding resulting from changes in the temperature thereof.

24. In an indicator, the combination including, indicating means,electromagnetic means comprising an armature winding for operating saidindicating means, a source of electrical energy for said electromagneticmeans, said source including an armature winding and a cooperatingmagnetic iiux producing rotor, said windings having positive temperaturecoeilicients of resistance, negative temperature coeillcient resistorslocated in proximity to the second-mentioned armature winding soconstructed and arranged as to compensate for the effect of temperaturechanges upon the system, and a substantially fixed annular ringsurrounding a portion ci the permanent magnet rotor and having acharacteristic such that its magnetism decreases substantially uponincreases in temperature, and vice versa, whereby said resistors andring are eflective tov compensate for the eil'ect of temperature changesupon the magnetism of said rotor and the resistance of said winding.

25. In apparatus or the type described, the combination' including,indicating means, electromagnetic means comprising an armature windingfor operating said indicating means, aA

ltemperature coeillcient resistance means located in proximity to thesecond-mentioned armature winding, said resistance means having acharacteristic such that the coeiilcient `ofresistance is m'eater inmagnitude in a lower than a bisher temperature range, and magnetic meanslocated in proximity to said rotor constructed ot metal, thepermeability oi which decreases substantially for unit variations intemperature in the higher temperature range, whereby the resistancemeans and magnetic means are effective to compensate for the effect oftemperature changes upon said rotor when said energy source is placed ina high temperature region.

26. In apparatus of theme described, the combination including,indicating means, electromagnetic means comprising an armature windingadapted to produce a revolving ux and an induction type rotor actuatedthereby for operating said indicating means, said winding having apositive temperature coeiiicient of resistance, and negative temperaturecoeicient resistance means vlocated in proximity to said electromagneticmeans adapted to undercompensate for variations in the resistance of thewinding occasioned by ambient temperature and current variations.

Homes n. incarna.

BEST AVAILABLE Coe 27. In apparatus o! the type described, thecombination including. indicating means, e1ectromagnetic meanscomprising an armature winding and an induction type rotor actuatedthereby for operating said indicating means, said winding having apositive temperature coei cient of resistance, and negative and positivetemperature coetiicient resistance means located in proximity to saidelectromagnetic operating means for compensating for variations in theresistance of the circuit occasioned by ambient temperature and currentvariations, said resistance means being so construed and arranged asconJointly to overcompensate for the effect of temperature variationsupon the resistance of said winding, whereby said resistors are eiectiveto compensate also for the effect of temperature changes upon saidinduction type rotor.

HORACE M. NORMAN.

" orcoaascfi'ron.

January 18, 19h11..

It 1s hsrebyeegejiripn error appears in che printed specification of theabove requiring correction as follows g ond column,v line 59,1 atrikeout the word in before the-- colmi, une. la', claim' rai that the s areco 212.81m were' (sealy *combinaison* read combinar second colunn'i@line 15', claim 27,-101' construed that the-said lettere Ifo-tent shouldber-eed with n fca cthsgreeord or the ease 1n the day-or April, A. D.19m.

Page 2, sec- ,.page l0, first ion; page 11, read -conatructed; and thiscorrection therein Patent Office.

Leslie Frazer or lmcnon.

Patent soga-559233. e j January 13, 191m.

"jff HQBACE M'. NORMAN. It ierhereby eertiried `error appears in theprinted specification of the above numberegl' peteit' requiringcorrection as follows: Page 2, sec.. ond column, line 59, strik-gout theword in before -the 5 page 10, first column, une 15, amm 11i,4 refr'emmanuel read -omb1nat1on, page 11.

second celu-:m1,l line 15, cleim 27,-for construed" read constructed;and that the'said Lettere Pate: `zfxhe'ull 'oe-read with this correctiontherein that the sne -mnyloenfom to the record of the case in the PatentOffice.

teigne@ une sealed anis 5th @y of April, A'. D. 19241;.

Leslie Frazer (Seal)I Acti-ng Commissioner of Patents.

